Journal of Applied Physiology, Vol 59, Issue 1 132-136, Copyright © 1985 by American Physiological Society

ARTICLES

Muscle performance and metabolism in maximal isokinetic cycling at slow and fast speeds

N. L. Jones, N. McCartney, T. Graham, L. L. Spriet, J. M. Kowalchuk, G. J. Heigenhauser and J. R. Sutton

To provide a description of the metabolic changes in muscle during maximal dynamic exercise, muscle biopsies were obtained in five healthy subjects before and after 30 s of isokinetic exercise at two pedaling frequencies (60 and 140 rpm) associated with contrasting fatigue characteristics. Higher peak power was attained at 140 rpm (1,473 + 185 W) (mean +/- SE) than at 60 rpm (1,122 +/- 70 W), but the decline in power during 30 s (fatigue index) was greater at 140 rpm (61.6 +/- 3.2 vs. 21.5 +/- 2.4%), total work in 30 s being similar (18.1 +/- 1.10 vs. 20.1 +/- 1.10 kJ). Changes in the concentration of muscle metabolites were similar; creatine phosphate concentration fell to approximately 50% of resting values, and the glycolytic intermediates glucose 6-phosphate, fructose 6-phosphate, and fructose 1,6-biphosphate increased up to 30-fold. Muscle lactate concentration ([La-]) was 29.0 +/- 3.98 and 31.0 +/- 4.31 mmol/kg wet wt immediately postexercise at 140 and 60 rpm, respectively. Even after only 10 s exercise (n = 2), large increases were measured in glycolytic intermediates and [La-]. In the two subjects, muscle [La-] increased to 17.2 and 15.1 mmol/kg at 140 rpm and to 14.3 and 14.2 mmol/kg at 60 rpm. In this type of exercise, glycogenolysis is activated very rapidly at both pedal speeds; the changes in glycolytic intermediates were consistent with rate-limiting steps at the phosphofructokinase and pyruvate dehydrogenase reactions. The greater fatigue at the higher speed is not accompanied by different biochemical changes than at 60 rpm.

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